On seeding equatorial spread F: Parallel or transverse transport?

There is considerable current interest in how the spawning of equatorial plasma bubbles (EPBs) is affected by the nature of the plasma-seeding process. The process most likely involves an atmospheric gravity-wave and coupling of its wind perturbations to the plasma in the bottomside of the F   layer. Neutral-ion coupling can occur either via transverse transport (TT) perpendicular to geomagnetic field (B→) lines, or via parallel transport (PT) along B→. Whether TT or PT is responsible is important, because each involves different physics, which could lead to substantial differences in EPB development. The general consensus, until recently, was that TT controlled both seeding and the EPB growth process. Evidence, however, has appeared in the literature, which seemingly supports the notion that PT is playing a role in the plasma-seeding process. In this paper, a clarification of the physics is presented, which show that TT is, in fact, the dominant seeding process.

► We evaluate two neutral-ion coupling processes as the source of seeding in equatorial spread F. ► We conclude that transverse transport, which produces large scale wave structure is most dominant. ► We conclude that parallel transport is not playing a primary role in seeding.